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Wurlitzer 4573C Hums (Buzzes) at startup

Hi, I recently acquired a Wurlitzer 4573C organ in good condition appearance-wise. They said it was playable, but sometimes had problems with the power supply. Since I got it, when I try to turn on the organ, it immediately hums really loud, and nothing changes no matter which button or pedal or key you press. Any ideas where to start in trying to get it going?

Loud hums are usually either grounding problems or capacitor problems, particularly in the power supply. As you've already been told that there are power supply problems, that's the most likely cause. I'd guess that you're going to be changing all the electrolytic caps in that area for starters. It is nearly 40 years old and you may end up changing a lot of electrolytics throughout the entire organ too.

I don't know your electrical/electronic skills but be aware that there are plenty of lethal voltages where you will be working. I'm sure that our regular electrolytic cap expert will be along soon to give you some expert advice. If not, or if you can't wait, then look up some of the many posts on the subject from indianajo.

It's not what you play. It's not how you play. It's the fact that you're playing that counts.

Yes, my 4500 hardly makes a sound, which looking at the schematic I blame on PS problems caused by dried up or shorted electrolytic caps. E-caps are aluminum cans full of water based compound, sealed with rubber in the cheaper ones. Organs have the cheaper ones. The rubber cracks after 20 years, used or not. Mine probably has other things damaged by the shorted caps - rectifiers or resistors or fuses. None of these parts are expensive, you just have to change them like mowing the lawn before the basswood trees take over.
You have one option on a Wurlitzer. You may remove the power supply chassis and send it to Morelock's for rebuilding. The freight is list price but the prices at Morelock's seem attractive. Morelocks is in Rienzi, Mississippi, an can be reached through mitatechs.org. Morelock's also sells the schematic diagrams. They also sell subassemblies, but I don't recommend these as another member found assemblies with the same part numbers did not have similar wire harnesses.
I put 71 e-caps in my H182 # 9574, and it change the sound from kazoo like to sparkly and deep.
You will have to change the smaller caps out on the circuit boards yourself. They don't dissasemble for shipment. If your going to buy the tools and learn how to solder, you may as well do them all, I feel. 71 caps was $200, but the 3 multisection cans were $120, and about $100 of that can be saved by installing individual radial lead caps on terminal strips under the chassis.
Unplug the organ and measure all caps (or any wires you touch) under the chassis as under 25 VDC to chassis with a DVM before touching it. Also, no jewelry, as even 6 VDC could burn your finger off if you wear a ring. Use a clip lead on negative to chassis, so you only measure voltages with one hand. See this thread about making a discharging tool if you have to discharge caps, but it is not likely you will need one. http://www.diyaudio.com/forums/instr...then-dead.html
See this article post #25 about the cheap way to buy long life replacement e-caps and how to install them. http://www.diyaudio.com/forums/instr...then-dead.html You won't be able to find mutl-section cans for a Wurlitzer at the transistor voltages, and besides they are not rated for service life like the radial lead caps are. Buy the long life ones and do it once in a lifetime- I've had to re-e-cap my hifi amp 3 times in 40 years of ownership.
Paying a professional is not really an option on something this old. Both the techs on here talk about replacing the "one that is bad". That is fine if you want an instrument with a mean time between failure of a month. Wurlitzers have very good key contacts and tab switches, so if you get all the old rubber out of there, they should go years between subsequent failures.
In the beginning, some other cheap PS components may be blown, like rectifiers or power resistors. You can report back with those problems. You can also educate yourself on standard power supply repair. Thomas Floyd Electronic Devices, the Electron Flow Version was a book I found at Goodwill for $2 abandoned by the local community college. Very useful on meter use and linear power supply design and repair. Your organ will not have switcher supplies.
Have fun.

Jo I will have to do a search for that book one of these days to add to my repair library. I'm always glad to see your advice and store in my "documents" files under advice in case I can't recall the thread. You are such an asset to the group. Many thanks Paul D

Hi, I recently acquired a Wurlitzer 4573C organ in good condition appearance-wise. They said it was playable, but sometimes had problems with the power supply. Since I got it, when I try to turn on the organ, it immediately hums really loud, and nothing changes no matter which button or pedal or key you press. Any ideas where to start in trying to get it going?

Sounds like you need to change the electrolytic can capacitors on the power supply and the rectifier diodes.

Okay, I rarely promote a business, but this one is actually the Wurlitzer factory- formed by former Wurlitzer employees, they know their stuff and they are cheaper than anyone else for the most part. Also they will help you narrow down the issue on the phone to the point of helping you know what to send them for repair if need be....
Morelock's Wurlitzer parts* in Mississippi has all of the NOS Wurlitzer parts in stock for over 170 Wurlitzer organs and pianos and is owned and operated ( including sales AND reasonable quality factory repairs. ie. In your 4573 they can rebuild the entire amplifier chassis for about $50 + parts. In terms of the electrolytic 'can' capacitors there are about 7 total ( 4 on one amp and 3 on the other- two amps...unless the 4573 had the two channel single chassis by then) and run about $10 ea., and the smaller electrolytic capacitors, about $.50 to $1 ea are mounted on the PC boards of the two amplifiers- about 15-20 of these. Morelock's recommends changing ALL of the smaller electrolytic capacitors on these two amp chassis because the black plastic tubing they are formed in tends to harden and become slightly distorted which tends to allow leakage on the positive end. I found that the smaller the value of these then the more tendency to fail. Like Hammond, Wurlitzer organs are easy to change out parts and doing it yourself is far better because you'll do it for less money and you will be learning a basic skill- how to maintain your instrument! Some people insist that they will never undergo fixing their organ because they are players, not repairmen, but when it comes to electronic organs you just might wait a long long time to get someone to come out and do the repair and you will pay at least $500 for what you could do yourself in a few evenings for about $80. If you can read, operate a wood burner, and made it through 8th grade math you are good to go.

The 4573 organ is a great organ and you will be rewarded with a very powerfully rich and versatile organ for many years when it's revamped. Morelock's also recommends changing the power supply diodes. $1. A must have is the service manual. Wurlitzer manuals are thorough and straight forward. You'll need a good ohms meter, soldering iron, small needle nose pliers, and small side cut pliers. Also get a solder sucker or solder braid to remove old solder for removing can caps and solder from PC boards when replacing parts.

There is a simple way to change out small capacitors without removing them from the PCB. Simply cut the old capacitor directly at the capacitor itself and bend a right angle straight up from the board on each side that was cut. Next, place new capacitor on board and wrap leads from the new capacitor with a loop parallel to the PCB, but around the right angle bend of the old part's leads, finally solder the loop and clip the right angle and the remainder of the loop.

One word of encouragement. You really only need to know some basics in order to do basic troubleshooting. First of all, when you read a schematic it is nothing more than a diagram of what parts go to what parts. With most organ service manuals you get the schematics that have numbers on each and every part on the schematic. For instance, right next to the transistor there will be TR1, TR2, and so on to correspond to the TR1,TR2, etc. on the 'parts layout' drawing. The parts layout is exactly what it sounds like- it is a drawing that looks exactly like the top view of the circuit board with all of the parts on it. Remember, there are only about 8-9 different electronic components in an organ or anything else electronic for that matter... So anyway, once you see where the part is at on the physical board you simply find the number and trace it back to the schematic. Then next to each diode, transistor, and transformer will be little voltage readings. A transistor will have 3 voltages. Coming out of the 'mains transformer' it to will have voltages. If you get your VOM ( volt ohms meter, yes you'll need a VOM too) then you can measure these voltages that correspond to the voltages on the schematic. If the voltage is not the same then you know you have a problem there. If other voltages in other areas also don't correspond correctly then you can fairly easily trace the fault back to a common point that these have in common. For instance, a Can capacitor will also have a voltage reading at it's + terminal ( or - terminal in a 'positive case' can capacitor) and changing the bad capacitor will correct the voltages going to the bad transistor reading. On occasion it's actually a bad transistor, but there are other tests that can be done. However, for your purpose of correcting a humming amplifier it should be fairly cut and dry.

Whatever you do, get a service manual. Morelocks sells them for $20. Jan Giradot might have one as well. Jan is on the Forum and you can probably send him a personal message or he will see this and let you know here.
Go on Youtube in the meantime and watch some basic electronic videos. You needn't be a technician to fix your organ, just a little patient and don't be afraid to ask questions.

I have this manual for sale from my collection:
4570-4572-4573-Orbit III @$10 + shipping
Like all my manuals, this is an original Wurlitzer factory-published document, not a xerox, scan or photocopy. If interested, contact me at jan@theorgangrinder.net

if it is a tube organ, it is the tubes warming up. they can take anywhere from 30 seconds to a few hours to warm up. if this is the case, this is what you are hearing. if not, it is most likely an input to a speaker touching a ground, and making the speaker hum.